Incandescent lamp and manufacture thereof



C. A. LAISE Sept. 17,

xucAuntscx-mr LMlP AND MANUFACTURE 'n'm'nnor' Filp d March 23. 1935 Patented Sept. 17, 1 940 UNITED STATES P A'TENT OFFICE LAMP AND- MANUFACTURE THEREOF Clemens 'A. Laise, Tenafl'y, N. 1., Fidelity Union Trust Company, executor of said Clemens A. Laise, deceased I t Application March 23, 1935, SerlalNo. 12,567 V '4c aim (01. 176-16) 1 ,INCANDESCENT This invention relates generally to improve ment-in high 'efllciency'incandescent'lamps, and especially to lamps of the character that utilize metallic filaments as light emitting. elements. ,An 7

important feature of the invention concerns a novel electrical circuit, preferably embodied in the lamp structure itself, which is adapted toprocluce a higher efilciency combined with longer life than is possible to attain with the lamps of the are as heretofore known. The invention is particularly concerned with the construction of such a-lamp and circuit and method of .making the same, which is especially well adapted for use in lamps produced in conformity with the principles hereproduced a shock sufficient in many cases-to rup ture the filament. g V

. It is an object of the present invention to provide a lamp capable of attaining the highest possible efficiency andwhich at the same time will be capable of preventing thesurge and consequent shock due to the switchingon of the current. I It is a further object of the invention to probide a lampof the high efilciency described that will have along commercial life. The elimination of the initial surge; of course, is the primary reason for this longer life, not only because with the elimination of the surge the shock is also in set forth. 1 eliminated, but also because a frequently observed 15 Y The expression high efficiency lamp as used phenomen p nying the sur e p i y in thepresent application needsa certain definiwhen t e filament is highly c n e t a ed, S the tion. It is probably true that-this term has been formation of an arc across the leads and the in use since the early days of the lamp art. It is concomitant destruction .of the filament at the 2o certainly true that with the introduction of me- Point of junction with the leads. v v l k tallic filaments, the lamps utilizing these filat Isa-st l further J O Pr 84131111) 0 7 ments became known as high efficiency lamps. high cfl y having lead .wires of small-diam- The term, however, had meaning only in cometer and hence with only'slight coolingzeifect parison with carbon lamps and other lamps ofupon the fila In lamps of h Present lesser efllciency. With the appearance of the 'the cooling effect of the:leads is sumcient to 25 tungsten filament lamp, the term acquired a new cause relatively large differences in temperature I meaning and when this was followed by the gaswith the highest temperatures m dway between filled lamp with a coiled tungsten filament, it he lea s. When su h di r nc s of temperawas thought that a lamp of this type was the tures exist, the filament frequently ruptures or high efllciency lamp. fuses at the exceedingly hot midway point.. 30 ,7 Developments of recent years have, however, To accomplish these objects of the l vcn n.

' shown still higher efiiciencies are possible, For, a Spe y designed Circuit 5 D O de in the whereas in former times each increase in efillamP- ciency was attained by use of an improved fila- The Preferred elements of the-Circuit above ment material or by use of'a more suitable ga'sesug comprise a filament 0f the Phys c 35 ous atmosphere, it has lately be 11 the aim to and mechanical structure hereinafter described; use the same gaseous atmosphere and the same a resistance element having resistance characfilament materlalliut to attain greater efiiciency t'elistics pposed t those of the fi a e d S by applying more exact engineering principles ficient to balance the initial current surge; and 40 tothe'lamp construction, Y leads of small diameter and high conductivity. 40

In the lamp art, efficiency consists in obtainsuch a circuit is represented diagrammatically ing the greatest amount of lumens per watt coni m 1 of the annexed d n In Flgssistent with a sufllciently long life to satisfy com-/ e 28 a {nustratFd crosssectlonal and mercial and practical needs. As efliciency is intudmal. sectwnal news of the fllamgnt; creased, the life'of the lamp is shortened, other and 4 Illustrate different ways in 'P the 45 things being equal. In the lamp art of the past Quit and filament maybe inqqrpomted m a stand' n m be t ibl m ard type of lamp; Fig. 5 shows a current-time g e S poss e C .ency w rare y curve of the initial operation of an ordinary lamp; attamed for h reason that such alarm) was not and Fig. .6 shows the current-time curve of a o Wen/adapted to sustain the shock of turning the lamp constructed in accordance with the inven- 5 u e on A metal filament 15 most'con 1 tion. Fig. '7 is an enlarged section taken along m when cold; but as the temperatul'ti'inthe line 1-4 of Fig. 3 showing the construction creases, the resistance also increases. There is, f t d i I 7 therefore, at the instant of switching on, a sud- The above described elements will be described 5 den surge of current through the filament which seriatim. First, the filament. The filament of a should be 'so wound that the magnetic effect due toithe lien of force generated about it will not 4 the lamp of this invention may be of the general type described and claimed in my Patent No. 1,631,493, consisting of tungsten as a base with additions of boron nitride or boron-suboxide and potassium borate which have a scavenging effect. The metallic bar from which the filament is drawn is so treated that at the sintering or metallizing temperature a portion of the scavengers distils out and takes along with it'detrimental" impurities that may be present in the tungsten base. The amount of such scavenger additions is a such that in the final filament the amounts remaining are very minute, being one-quarter; of

one per cent. or less.

relation to its length. The filament metal is relatively soft and pliableand the section boundaries interlock laterally and-longitudinally of the wire in such a manner that the filament neither 'sage,*ofisets nor ruptures, and-the intergranular cement being reduced to a minimum, the filament H v has "little tendency .to .twist. or distort after it has been shaped and set into, suitable conceni V I One. prime .cause of brittleness in tungsten filae trated form.

" ments of the granular type of the prior art, is the presence of foreign non-metallic substances in the grain boundaries. For instance, in the old pressed .-filament.as. first produced, additions of variousv substances-such as theoxides of calcium, aluor-squirted tungsten filaments, anprganic binder :was used which became carbonized during the the crystal boundaries. -In the, drawn tungsten .minum or thorimn,:were added for the purpose of retardingthe growth of crystals. This practice resultedhalso in compounds in the grain boundariesthat tended to produce a brittle filament, particularly after a short period of use.

In the. later,.so.-called non-sag tungsten filament I additions are made to themetal that produce silicon compounds and probably also hydride's in. the grain boundaries with aresulting brittleness "after relatively short use. q r 1 All such intergranular substances act solely as cements. holding the grains together and prevent-;

. t0 the, tungsten powder from which the slugs are made and from which they are drawn down to ing the grains from coalescing and forming larger grains. In the filament of the present invention,.however, the -cementing material is composed of scavenging substances which are added filament diameters; After the addition of the scavenging material to, thepowder, the same is worked into-slugs in the usual way and the conditions-of manufacture and heat treatment so regulated that they-.have agrain count of approximately 15,000 to 20,000 grains persquare millimeter, v

The slugs are mechanically worked by swaging and drawing into wire and then concentrated into coils or coiled-coils or rolled into ribbon and corrugated or twisted into concentrated'f orm. In

:10. v soluble in acids may be usedand the coil or-coiled-' making coiled coils of filament wire, the wire cause short circuiting.-

When maldng coils or coiled-coils, mandrels of nickel or nichromeor other refractory metals 'coil is heated on the mandrel preferably in an atmosphere of wet hydrogen attemperatures ranging from 1000 -C; to 1500" 6'. until a per manent set is imparted to the filament and the sirable.

wire has been relieved of all of its strain. Thus, there will be no readjustment of the coil after the mandrel is dissolved out.

I use wet hydrogen, a practice contrary to that of the present art in which dry hydrogen is used in such operations, for the reason that wet hydrogen tends to decompose carbides on the surface or in the grain boundaries of the filaments. II dry hydrogen is used, carbides'are likely to form with the filament metal in the presence of carbon or carbon compounds. As a result of my process employing wet hydrogen, the pliability and ductility of the filament is not impaired as it would be if dry hydrogen were used.

The heat treated coil and mandrel are then cut 'to proper lengths to give the proper voltage of lamp and'the mandrel is then dissolved in suitable acids such as nitric acid and sulphuric acid it nickel or nickel alloys are used as mandrel wire.

" After the coil or other shape of filament treated in theabovemanner is mounted into the lamp, the lamp is sealed and exhausted or filled with gas and then flashed by connecting, the lamp in series with a rheostat. or nichrome resistance at about .over voltage that is 125% of the rated voltage of the filament fora period of about five minutes, so that thefilament quickly attains the germinating temperatures and the grains coalesce or fiowinto each other, producing a light emitting medium with long interlocking' sections which have little tendency to sag or "distor t.' Such sectionsmay consist of at least one turn and preferably severalturns .of coil,

especiallyafter' the lamp has lburned. about one "takes place across the lampand 75% in'the balance of the circuit consisting of a suitable rheostat.

' During the heat treatments above described, the scavenging materials ten'dto distil out, carrying with them substantially all impurities, ineluding occluded hydrogen, that may be present in the grain boundaries. With these impurities eliminated, there is little obstruction to rapid grain growth and the formation in-the filament of long sections and but few interlocking section boundaries. Instead of the particular scavenging materials mentioned, other refractory nitrides may be used with excellent effect, such as barium nitride or beryllium nitride.

InjFigs. 2 and 2"a1"e, illustrated enlarged sec.-

tions of a'straight filamentcomposed of inter It is apparent that this filamentof few interlocki'ng'se'ctions can be operated at a much higher efliciency or lumen output and longer life than a highly crystallized filament I of many grain boundaries. Furthermore, it retains its shape after it is once permanently set or flashed by my special process in'the lamp circuit of this invention, so that it does not droop, shrink, twist or short-circuit between the individual sections.

lamps, especiallyof the higher voltage type, a

concentrated form such as a coiled coil is de- In-every'case, however, my principle of looking sectionss and III, which are representativeof .thefilame'nt structure above described.

5 treating operation after the lamp is exhausted to produce the final strucelementas previously or even after it is based ture in my light. emitting set forth.

The second feature oi my lamp .that the 1 filament is preferably mounted upon lead. wires of the general type desc bed and claimed in the copending application of CIemens. A. Laise and Jacob Kurtz, Serial No. 70 7.106, but the diameter of these lead wires, by virtue of the exceptional '15 heat and current conductivityaoharacteristic's of.

the material thereof, maybe made much smaller than that generally used in lamps of the-present art of equivalent wattage and may beas small as 50% of the cross-sectionai area ot the go of such generally used lamps. i

The wire described and claimed \in said copending application may be described generally as being composed of a nickel sheath and a copper core, the nickel constituting a relatively large 25 proportion of the thereof. In cross-section such a wire appears as indicated inthe enlarged view of Fig. 'I.

A third and very important feature of my invention is that the resistance or ballast disposed in the circuit is incorporated in one of the leads, either within the stem as indicated at IS in Fig. 4, or without it asshown at I in Fig. 3; or it may even be arranged outside of the lamp. I

The purpose of this ballast or resistance is to 35' eliminate the sudden surge of current through my "lamp. It may consist of a small choke coil or similar device which momentarily has aihigh resistance when connected across a difference of potential and then, as the current begins to 40 flow, the resistance is practically eliminated so that the loss of power due to the presence of the same is practically negligible. a

This coil or equivalent r bedded in metallic oxide and may or may not be 45 enclosed in a seramic, or resinous, -"or Bakelite composition whichholds it in. place and insulates it both electrically and thermally. ;lhe conducting oxide may be iron; oxide or other equivalent oxide or conducting material which has a high resistance when cold and becomes very conductive when heated up slightly.

The surge preventive in my directly into the circuit of the incandescent lamp either inside of the bulb, which I prefer, or out- 55 side of the bulb. It may, however, also be placed into the lamp base or into a socket into which the lamp base fits.

The circuit of my improved lamp with the ballast included as surge-preventing medium is such that the initial resistance of the circuit is greater than the normal operating resistance of I the circuit of the lamps now in use or so that the initial flow of current is less than the normal flow 0! current in the same lamp when operating at lead wire curves with ciirrent total wire and at least istance may be im- I invention is placed its rated voltage. This is illustrated by the curves Fig. 5 which indicate the initial surge of the lamps I of the present art, and Fig. 6 which indicate the initial per ormance of a lamp of the present inventionr I The resistance or ballast is such that it does not caus'e'substantial loss of power in the circuit duringthe normaloperation but merely dampens, reduces and tends to prevent the initial surge of current whenthe' circuit is first connected across a difference-in potentiaL' tards the sudden rupture of filament at the grain boundaries and also reduces possibility of arcing,

across the lead wires.

Figs. 5 and 6 above referred to are comparative plotted against time showing the eiiect of the circuit oi. thepresent invention.

[In Fig. 5 the initial surge of current introduced into an ordinary lamp is considerable but is :quickly reduced to a seconds. In Fig. 6 the initial current introduced into a lamp constructed in accordance with the principles of the present invention is shown to rise gradually to a constant value after a few seconds and the usual surge is substantially avoided. i

Having thus described my invention, what I claimisz 1. An incandescent lamp comprising in combination an envelope, 9. base, a coiled coil tungsten filament, lead-wires connecting said filamentto said base, said'lead wires being of relatively small diameter and consisting of a nickel sleeve on a copper core and an electrical resistance in one of said leads said resistance having a negative coeflicient of resistance. I

v2. An electric incandenscent lamp comprisin in combination, an envelope, a base, a tungsten filament, relatively light composite lead wires consisting of a nickel sleeve on a copper core connecting said filament to said base and an electricaliresistance in series with said leads said 3. An incandescent lamp comprising in combination a concentrated light-emitting body composed of tungsten having long interlocking grains, leads connected thereto having relatively slight cooling power, and a resistance element incorporated in one of said leads, said element consisting of a choke coil embedded in metallic oxide.

4. An incandescent lamp comprising in combination a concentrated light-emitting body composed of tungsten having leads connected thereto having relatively slight cooling power, and a resistance element incorporated inone of said leads, said element consisting of a choke coil embedded in metallic oxide embedded in an electrical and thermal insulating body.

, CLEMENS A. LAISE.

I This eliminat .tion of sudden surge of current prevents or relong interlocking grains,

constant value after a few I CERTIFICATE OF CORRECTION; Patent No. 2,214,711.12; pt mber 17, 191w.

ems-A. Lust. It is hereby certified that error appears in the printed specification "ef the above qmnbered patent requirihg correction as follows: Page 1 first column, line 9, for "are" read --art-'-; page 2; first coimen, line 21, for

uu'zn', line 11.5, for "aerami'c" read -ceramic--; and aecor 1d column, line 58,

"Cla m 2,- for "incandenseent" read "incandescent"; linewh, same claim, for tofficience read -c'o eff1eiente; and that the ae-id Letters Peten't should be read filth thie correction therein that the same may contom to the rec I 0rd of the case' inthe Patent Off ice. Signed and seeled this 15th day of October, A. D. 191m.

, Henry Van Arsdale,

fiscal) Acting Commissioner of Patents.

sage" read "sags"; line 67, for "lien" read --line---; page 5, first 001- 

